Spray device actuated by supersonic means



April 1959 .1. SEDLACSIK, JR 2,831,092

SPRAY DEVICE ACTUATED BY SUPERSONIC MEANS Filed Dec. 10, 1956 INVENTOR.

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m e p United States Patent C SPRAY DEVICE ACTUATED BY SUPERSONIC MEANSJohn Sedlacsik, Jr., Garfield, NJ. Application December 10, 1956, SerialNo. 627,265 8 Claims. (Cl. 117-93) My invention relates to improvementsin an apparatus for applying a liquid coating material to an article ortarget by electrostatically charging and depositing the comminutedcoating material upon the article or target Within an electrostaticfield created between the article or target to be coated and the issuingsource of the coating material. That is, it relates to means forimparting an electrical charge to fluent coating materials, saidelectrical charge being such that when the material is atomized,precipitated, and dispersed, the charged spray is smoothly depositedupon the object toward which the atomized material is directed.

More particularly, the invention embraces means for spraying fluentcoating materials by employment of supersonic vibrational waves whichstrike an exposed surface or film of the fluent coating material.

The invention relates to the formation of a paint spray or similar sprayfrom a liquid material capable of relatively rapid atomization byexpelling the liquid from a reservoir or issuing source in which thematerial is held in liquid form. This is accomplished through the use ofa motive agent, such as air, in conjunction with an electrostaticattraction toward the distant article or target.

As is well known, small particles, when electrified by charges of likesign, repel one another, whereas particles of opposite sign are mutuallyattracted.

This invention is directed to means for improving this dispersion anddeposition of the atomized particles from a charged gun mechanism uponan oppositely charged article, such means providing greater stability tothe projected spray or jet and imparting a sharper edge definition tothe issuing pattern.

It is now known that compressional supersonic waves from apiezo-electric quartz or other crystal exert a unidirectional pressureat the surface of a liquid. Strong supersonic motions or waves in aliquid, as the waves arrive at an exposed surface, are rectified orconverted into unidirectional motions up out of the main body of theliquid, whereby supersonic waves may be used to cause unidirectionalflow of liquids, which unidirectional flow may be modulated bymodulating the strength of the waves.

Herein, a novel apparatus is provided for the spraying of a liquidmaterial in a fine, mist-like jet in response to the action ofsupersonic vibrational waves which are caused to strike upon an exposedsurface of the liquid.

A source of electrostatic high potential, having one terminal groundedand its opposite terminal connected to the atomizing head of theinvention and any metallic element connected thereto, creates a strongelectrostatic field between the head and the article to be coated, whicharticle is also grounded.

Energy imparted to a liquid by ultrasonic excitation no matter howstrong will not cause the liquid to break into a mist unless thecavitation threshold is exceeded. High electrostatic stresses on thesurface of the liquid may reduce this cavitation threshold, but thecavitation process ice produces the mist, not the compressional waves orunidirectional motion in the liquid.

The unidirectional flow in the liquid may be used to advantage asapplied herein producing a mixing action so as to prevent a non-uniformdistribution of paint or the like on a fiat surface. In this case, itwould counteract the tendency of the paint to break up under highelectrostatic stress into small drops as a result of the mutualrepulsion of small particles with like charges. However, concentricrings of paint would still occur at the nodal points of standing wavesproduced on the vibrating surface.

To produce the fine mist at cavitation levels, the high intensity ofsound must be concentrated at a point or a line by some acousticalfocusing device. At low ultrasonic frequencies this can be accomplishedwith a horn" or velocity transformer. At high ultrasonic frequencies,the transducer can be shaped into a spherical concave surface to focusthe sound at the surface of the liquid in which it is immersed.

When cavitation occurs, small vapor-filled bubbles are formed in theliquid, and as these bubbles collapse or implode, the shock-waves thusgenerated set up large disruptive forces at the surface, which causesthe liquid to break up into a fine mist.

In this invenion, the coating material is normally supplied to thedischarge spout, a pan fastened thereto, and its region of coronadischarge at a rate at which it can be electrically atomized by thecorona discharge most efficiently and effectively, after which thecharged particles are projected in spray form toward and deposited uponthe oppositely charged article.

Depending upon the viscosity and other characteristics of the material,and depending also upon the rate at which the sprayer is modulated sothat the unidirectional flow is accordingly modulated, the control ofthe supply is such as to permit the discharge of precisely the correctquantity and size of particles so as to effect the greatest etficiencyin coating a surface.

These objects I accomplish by means of such structure as will fullyappear by a perusal of the description which follows and by variousspecific features which will be hereinafter set forth in connection withthe drawings wherein:

Fig. 1 is a diagrammatic view of the apparatus embodying the novelfeatures of the invention; and

Fig. 2 is a plan view of the coating distributing plate or pan of theinvention shown in association with one form of nozzle for delivering amotive agent such as air and a fluent coating material such as paint tothe plate.

In this drawing, I have illustrated a complete example of one physicalembodiment of the invention. It will however be understood that changesand alterations are contemplated and may be made within the scope of theclaims, without departing from the basic principles of the invention.

Referring now to the drawing more in detail, in which similar charactersof reference indicate corresponding parts in the several figures, andreferring more particularly to the preferred form of my inventionselected for illustrative purposes, I have shown a horizontallypositioned nozzle, generally designated by 2. By means of the head 2 anda pan P attached thereto, the liquid coating material may beelectrostatically atomized.

Such a nozzle is similar to that shown and described in an applicationfiled by John Sedlacsik, Serial Number 468,670, on November 15, 1954.

The liquid coating material is led from a source (not shown) to the rearend of the nozzle 2 and likewise the motive agent is led from a source(not shown) to the rear end of the nozzle 2.

Said liquidcoating material and motive agent are dis- 3 charged from theforward end of the nozzle 2 onto a platle3 or pan P, having a knife edgeforwardly, indicated at The pan P is secured in a suitable manner to theforward end of the nozzle structure.

The nozzle is arranged so that a pair of spaced lips 4 and 4 at theforward end thereof provide a slit or mouth or opening therebetweenthrough which the liquid coating material emerges.

The uppermost lip 4 is disposed slightly above the plane of the pan P soas to provide a somewhat wide and relatively thin stream of liquidcoating material onto the rear end of the pan P.

A motive agent conducting tube 6 may be disposed within the head 2 andmay extend through an appropriate opening in the wall thereof so as toprovide a free outer end which may be disposed closely adjacent one ofthe lips 4.

In actual operation, the supply of electrical energy is fed to the highpotential nozzle assembly. The coating material being atomized and themotive agent are delivered through the respective delivery tubes andconnections to the head assembly and the pan. The coating material andmotive agent are released in the form of high velocity streams wherethey meet and mix with each other under pressure and are atomized andelectrically charged at the outer edge 10 of the pan, passing outwardlyinto the field with high turbulence.

In prior art arrangements, the projected jet wavers erratically,resulting in a scattered dispersion of the particles comprising the jetand causing the deposited pattern upon the article to have irregularlydisposed lakes. In addition, the mutual electrical repulsion of theparticles due to their being charged to the same sign causes them tospread and scatter laterally, particularly at the outer portions of thejet. This makes a less sharply defined edge at the boundary of thedeposited pattern, than is desirable.

To overcome these objectionable characteristics, I provide a gaseousfield surrounding in close proximity the electrostatic atomizing fieldand coextensive in length with the latter. That is, it extends along thelip with which it is substantially coaxial and terminates at the surfaceof the article to be coated.

In this manner, an air envelope is provided adjacent the outer peripheryof the lip whereby a gaseous medium of any desired nature may beintroduced around the stream of coating, being dispersed through themouth so as to surround or envelope the same.

By the use of this gaseous envelope outside of and surrounding theliquid, the paint or other material being sprayed with the apparatus maybe better concentrated or dispersed over a given area of the articlebeing coated.

By means of this concentration of air around the liquid, the center ofthe area being sprayed receives as much of the sprayed material as theouter edges thereof, the air blast having the capability of directingthe sprayed material inwardly toward the central area if desired.

The delivery edge 10 of the pan presents toward the articles to becoated a thinned or relatively sharp edge or discharge line, from whichthe coating material may be Withdrawn in the form of particles, therebyaiding the electrostatic deposition.

The liquid and gaseous materials are supplied through their respectiveconduits to the nozzle assembly as previously described. These materialsissue from their respective orifices at the outermost free end of thenozzle in the form of streams where they mix with each other. Theresulting mixture is directed outwardly from the pan edge 10 with highturbulence in the form of a finely atomized stream.

In operation, a unidirectional electric potential is ionizing effect ofthe corona discharge from the pan whereby the finely divided particlescomprising the spray are each imparted electrical charges of likepolarity and of substantially equal potential with respect to theatomizing lips.

The positively charged particles tend to repel one another and thusresist coalescence, with the result that the electrified cloud spray isattracted to the adjacent grounded article desired to be sprayed and/orcoated. The particles are attracted to and precipitate in a layer uponthe nearest surface of the grounded article which is to be coated.

Coating material is urged forwardly to the discharge lips and the panwhere it is electrostatically atomized and precipitated upon the articleplaced before the head by the action of the electrostatic field whichexists between the article and the head. The particles areelectrostatically dispersed as they are formed or produced along thethin line of atomization and they are electro-' statically depositedwhile still in the liquid state upon the article surface so as to form afinished coating.

As aforesaid, the spray head and pan are connected to a source of highvoltage R through one terminal thereof. The other terminal of the sourceis grounded and through ground is connected with the article to becoated to the end that the space or field between the spray head, panand article to be coated is electrostatically charged.

The electrostatic forces act on the coating material, causing it to bebroken up into finely divided or minute particles of coating material,so as to be attracted to the grounded article for deposition thereon.

The grounded article is referred to as a collecting electrode of onepotential with the applicator head and pan serving as a dischargeelectrode of opposite potential.

The electrostatic forces set up in the field between the electrodestransmits the finely divided particles of the coating material from oneelectrode to the other.

The same action will take place when the spray head and pan are groundedand the article is directly connectedwith the source of high voltage andis charged at a high potential.

With voltage applied directly to the spray head structure, a coronadischarge is formed in the region at the pan edge 10 and adjacent theoutermost periphery thereof and is of an intensity sufficient to breakup or to atomize into mist form the coating material and to project thecoating material in a spray form toward the surface of the article beingcoated.

The pan P is formed from relatively thin metal and may have relativelydiverging and forwardly extending side walls 8.

A forward transversely extending delivery edge 10 of the pan P is sharp,somewhat in the nature of a knife edge. The pan is formed from suchmaterial that it may vibrate at extremely high frequency. Particularlyits terminating edge 10 should vibrate at a frequency of severalthousand kilocycles.

A barium titanate or other suitable crystal C having a natural frequencyof several thousand kilocycles is provided and has an upper side securedin electrical contact with the lower side of the pan P.

A rectifying power supply is represented by R for supplying directcurrent voltage of one hundred-thousand volts or so from an alternatingvoltage of conventional power lines, such as to 250 volts, representedby 12.

The negative terminal of the power supply is connected by wire 14 to thenozzle 2 and thereby to the pan P, and to the lower side of a piezoelectric crystal C.

An oscillator of well known form is represented by O and is connected bywires 16 to an AC. power line.

An impedance-matching transformer is represented by T, the primary 18 ofwhich is connected to the oscillator O. The secondary 20 of thetransformer is connected by 22 to the power supply negative terminal andby wire 24 to the bottom or free side of crystal C.

A metal enclosure is represented by 26, which may enclose the powersupply and oscillator and preferably these components may be submergedin oil.

The positive of the power supply R is connected by wire 28 to theenclosure 26, and to ground, as indicated.

An article to be coated is represented by A and is connected to ground,as shown.

In operation of the apparatus, oscillation of the crystal C is broughtabout by the oscillator connected thereto, so that the plate P isvibrated, at the same supersonic frequency.

The supersonic frequency of the crystal oscillations results in suchhigh frequency of vibrations of the pan that coating material at thefree edge thereof is broken up into a very fine mist, as distinguishedfrom globules resulting from a spraying operation.

Alternatively to piezo-electric means for producing the supersonicenergy herein employed, the magnetostrictive, electrodynamic, fluiddynamic and hydrodynamic oscillator systems could be likewise employedso as to accomplish the results herein recited.

The piezo-electric, magnetostrictive, and electrodynamic systems canactually be coupled to the device as shown. The other two aforementionedsystems are means of imparting supersonic energy to the vapor or liquidphase by a jet or whistle action in the fluid or vapor, both of whichsystems can be used in this process.

The foregoing reveals the gist of my invention whereby others can, byapplying current knowledge, readily adapt it for various applicationswithout omitting features which, from the standpoint of prior art,fairly constitute essential characteristics of the generic or specificaspects of this invention.

I claim:

1. Apparatus for coating an object by spraying an electrostaticallycharged liquid in a fine mist-like jet on said object, comprising nozzlemeans for projecting a mixture of the liquid and a motive agent, meansfor receiving the projected mixture of the liquid and motive agent fromsaid nozzle means, said latter means being capable of supersonicvibration and having a free forward knife edge, means for supersonicallyvibrating said receiving means so as to apply compressional waves at asurface of the mixture of the liquid and motive agent discharged ontosaid receiving means, and means including a high-voltage sourceelectrically connected, respectively, to said receiving means and to theobject to be coated for maintaining an atomizing electrostatic fieldadjacent the free forward knife edge of said receiving means.

2. Apparatus for coating an object by spraying an electrostaticallycharged liquid in a fine mist-like jet on said object, comprising nozzlemeans for projecting a mixture of the liquid and a motive agent,pan-like means capable of supersonic vibration for receiving theprojected mixture of the liquid and motive agent from said nozzle meansand having a free forward knife edge, piezoelectric means for supplyingsupersonic vibrations to said pan-like means so as to set upcompressional waves at a surface of the mixture of the liquid and motiveagent discharged onto said pan-like means, and means including ahigh-voltage source electrically connected to said panlike means and tothe object to be coated, for maintaining an atomizing electrostaticfield adjacent the free forward knife edge of said pan-like means.

3. Apparatus for coating an object by spraying an electrostaticallycharged liquid in a fine mist-like jet on said object comprising nozzlemeans for projecting a mixture of the liquid and a motive agent,pan-like means capable of supersonic vibration for receiving theprojected mixture of liquid and motive agent from said nozzle means andhaving a free forward knife edge, magnetostrictive means for applyingsupersonic vibrations to said pan-like means so as to set upcompressional waves at a surface of the mixture of the liquid and motiveagent discharged onto said pan-like means and means for maintaining anatomizing electrostatic field adjacent the free edge of said pan-likemeans.

4. A coating system including a spray gun and a knife edged pan ofvibrating metal projecting forwardly therefrom, said gun being arrangedto discharge a liquid and a gas on the rear of said pan, and the forwardknife edge of the pan being adjacent an object to be coated, a source ofhigh potential direct current connected between said pan and saidobject, a piezo electric crystal having one side fastened to the bottomof said pan, and a source of supersonic frequency electrical currentconnected between said pan and the other free side of said crystalwhereby said pan is vibrated supersonically and an elec trostatic fieldextends from the free knife edge of the pan towards the object to becoated, both forces cooperating to produce an extremely fine mist-likecoating spray.

5. A system for spray coating an article with a liquid, including aspray gun fed with the liquid and a gaseous propellant, a vibratilemetal pan attached to the discharge end of the gun so as to receive theliquid propelled thereon from the gun, and having a knife edge at theend nearest the article to be coated, a piezo electric crystal attachedto the bottom of the pan, a source of supersonic frequency electricalenergy connected to the crystal and a source of high voltage directcurrent connected, respectively, to the pan and the article to becoated, whereby the knife edge of the pan is simultaneously subjected tosupersonic vibration and to corona discharge, so as to atomizc theliquid when leaving the knife edge of the pan.

6. Liquid coating apparatus including a forwardly sharp-edged pan, anozzle for spraying said liquid on said pan at a point remote from thesharp edge thereof, a source of high voltage direct current having theoutput thereof connected respectively to said pan and to an object to becoated with liquid, a piezo-electric transducer mounted in mechanicalcontact with said pan and a source of high frequency alternating currentconnected to the input of said transducer, whereby said liquid pan issupersonically vibrated and a simultaneous corona discharge appears atthe edge thereof, so that said liquid is simultaneously atomized to avery fine mist and impelled to the object to be coated.

7. The method of liquid coating with adjuvant electrical forces,including the steps of discharging the liquid into air in the form of athin fiat film, supersonically vibrating said film, and simultaneouslyapplying thereto a high voltage gradient in the direction of an objectto be coated.

8. Liquid coating apparatus including a forwardly sharp-edged pan,nozzle means for spraying said liquid on said pan at a point remote fromthe sharp edge thereof, a source of high voltage direct current havingthe output thereof connected respectively to said pan and to an objectto be coated with liquid, transducer means mounted in mechanical contactwith said pan and a source of high frequency alternating currentconnected to the input of said transducer, whereby said liquid pan issupersonically vibrated and a simultaneous corona discharge appears atthe edge thereof, so that said liquid is simultaneously atomized to avery fine mist and impelled to the object to be coated.

Hansell June 27, 1950 Miller Mar. 5, 1957

1. APPARATUS FOR COATING AN OBJECT BY SPRAYING AN ELECTROSTATICALLYCHARGED LIQUID IN A FINE MIST-LIKE JET ON SAID OBJECT, COMPRISING NOZZLEMEANS FOR PROJECTING A MIXTURE OF THE LIQUID AND A MOTIVE AGENT, MEANSFOR RECEIVING THE PROJECTED MIXTURE OF THE LIQUID AND MOTIVE AGENT FROMSAID NOZZLE MEANS, SAID LATTER MEANS BEING CAPABLE OF SUPERSONICVIBRATION AND HAVING A FREE FORWARD KNIFE EDGE, MEANS FOR SUPERSONICALLYVIBRATING SAID RECEIVING MEANS SO AS TO APPLY COMPRESSIONAL WAVES AT ASURFACE OF THE MIXTURE OF THE LIQUID AND MOTIVE AGENT DISCHARGED ONTOSAID RECEIVING MEANS, AND MEANS INCLUDING A HIGH-VOLTAGE SOURCEELECTRICALLY CONNECTED, RESPECTIVELY, TO SAID RECEIVING MEANS AND TO THEOBJECT TO BE COATED FOR MAINTAINING AN ATOMIZING ELECTROSTATIC FIELDADJACENT THE FREE FORWARD KNIFE EDGE OF SAID RECEIVING MEANS.